After a tumultuous three year term, DDB’s Chicago president Rick Carpenter has resigned. During the search for his replacement, Mark O’Brien, DDB’s North America, will serve as Chicago’s interim chief.

DDB Chicago has a number of Fortune 500 clients, including McDonald’s and Anheuser-Busch. DDB is part Omnicom, a global media and communications company.

Carpenter’s stint was marked by the tragic death of the office’s chief creative officer in 2008, and a two-year search for his replacement. During that time, the firm lost a sizable amount of business, including chunks of its Wrigley and State Farm accounts.

Carpenter said he resigned after much consideration.

“I am extremely proud of my tenure and accomplishments at DDB in both LA and Chicago and I have been fortunate to work with so many wonderful people and extraordinary talents during my time at DDB,” said Carpenter, who will stay on through the end of the year.

This is the second high-level resignation in two weeks. O’Brien, formerly chief operating officer, replaced Dick Rogers as North American president.

“I strongly believe in Ewan’s vision for the agency, and my primary goal in the coming weeks will be to lead the changes necessary to make that vision a reality and to remove any barriers between our people and the best creative work in the industry,” O’Brien said in a statement.